Process for producing liquid fuel from carbon dioxide and water

ABSTRACT

A process for producing high octane fuel from carbon dioxide and water is disclosed. The feedstock for the production line is industrial carbon dioxide and water, which may be of lower quality. The end product can be high octane gasoline, high cetane diesel or other liquid hydrocarbon mixtures suitable for driving conventional combustion engines or hydrocarbons suitable for further industrial processing or commercial use. Products, such as dimethyl ether or methanol may also be withdrawn from the production line. The process is emission free and reprocesses all hydrocarbons not suitable for liquid fuel to form high octane products. The heat generated by exothermic reactions in the process is fully utilizes as is the heat produced in the reprocessing of hydrocarbons not suitable for liquid fuel.

FIELD OF INVENTION

The present invention is broadly within the field of energy conversionand relates to processes for producing hydrogen by electrolysis ofwater, processes for reacting hydrogen with carbon dioxide for producingmethanol and/or producing syngas and processes for synthetic liquid fuelproduction.

BACKGROUND OF THE INVENTION

There are four global issues of concern that are addressed by thecurrent invention;

-   -   i) The diminishing capacity of the world production of mineral        oil;    -   ii) The effect of the increasing carbon dioxide emission on        global warming;    -   iii) The contribution from combustion of sulfur-containing fuel        to acidification of rainwater;    -   iv) The effective and economic utilization of available        renewable energy sources may not be suitable for conventional        applications.

Current evaluation of the world oil production predicts the productionto peak around the year 2010. As the world production capacity isbelieved to behave like a bell curve the expectations are that we willhave diminishing production capacity within a few decades from now.Demand on the other hand rises rapidly and it has become foreseeablethat in fairly short time, gasoline production will not meet demand.

It is therefore very important to develop processes that allowutilization of alternative energy sources to provide fuel that canimmediately substitute the currently used gasoline and diesel distilledfrom petroleum oil. Such fuel which is compatible with combustionengines as they are today will render the need for major, timeconsuming, technical developments and infrastructural changesunnecessary.

Currently, two processes have been used on industrial scale to producesynthetic liquid hydrocarbon fuel. One is the SASOL process which isbased on classic Fisher-Tropsch chemistry and converts coal to syngas,which is converted to a variety of hydrocarbons via the Fisher-Tropschsynthesis. The other is the Mobil Methanol-to-Gasoline process (MTG),which was utilized on large scale in New Zealand to convert natural gasto high octane gasoline fuel.

Syngas or synthesis gas is a term used for gases of varying compositionthat are generated in coal gasification, steam reforming of natural gasand some types of waste-to-energy facilities. The name comes from theiruse in creating synthetic petroleum for use as a fuel or lubricant viaFischer-Tropsch synthesis. Syngas consists primarily of carbon monoxideand hydrogen, and can be produced from natural gas through steamreforming: CH₄+H₂O→CO+3 H₂,

partial oxidation: CH₄+½ O₂→CO+2 H₂,

or combination of both.

The Fisher Tropsch process was developed by the German researchers FranzFisher and Hans Tropsch in the 1920s. It is a well documented processthat has been used on industrial scale for production of diesel andother synthetic petroleum products for decades. This process is used bya number of companies today to produced low-sulfur diesel and otherpetroleum products on large scale. For example, SASOL has implementedthis process since 1955 to produce petroleum fuel, AMSOIL introducedtheir first synthetic diesel in 1975 and since 1993 shell operates a14700 bbl/day GTL plant in Malaysia.

The conversion of syngas, obtained from natural gas, to methanol is avery well documented process. The process has been run on industrialscale for decades and the world production of methanol from natural gasis now around 30 MMtpa (million metric tones per annum).

The conversion of methanol to gasoline using the Mobile methanol togasoline process (MTG) is a viable alternative to the Fisher-Tropschsynthesis when converting syngas to liquid fuel. This process, where thesyngas is first converted to methanol and the methanol is converted in asecond step, over dimethyl ether (DME) to high octane gasoline, wentfirst on stream in New Zealand in 1985 and was producing about 14,500B/D a year later. Since 1997 the New Zealand facilities are usedexclusively for methanol production.

The global carbon dioxide emission has grown enormously in the past 50years. In 1950 the global emission was about 1000 million tons carbonequivalent, but has now reached close to 10,000 million tons carbonequivalent. About one fourth of this is industrial emission. As aconsequence thereof, the concentration of carbon dioxide in theatmosphere is generally estimated to have increased about 30% frompre-industrial times. Due to the greenhouse effect of carbon dioxide,this enormous emission and increased levels cause increasing concernabout the consequences of global warming.

It is therefore an important challenge to develop a process that allowsrecycling carbon dioxide to a valuable product such as liquid fuel. Itis even more beneficial to develop a process to recycle carbon dioxideto a liquid fuel that is equivalent or even superior to the currentlyused gasoline and diesel, and can substitute these without any need fortechnical or infrastructural changes.

To date, commercially viable solutions have not been provided forproducing liquid fuels from carbon dioxide and water. The presentinvention seeks to address this problem by a novel combination ofseveral processes for conversion of electrical energy to chemical energyin the form of synthetic liquid hydrocarbon fuels that can readilyreplace conventional liquid fuels from natural oil reserves.

SUMMARY OF THE INVENTION

The present invention provides a integrated, emission-free process forconversion of carbon dioxide and water to liquid fuel, such as highoctane gasoline or diesel, suitable to drive combustion engines. Theprocess may also be used to produce other hydrocarbons or hydrocarbonmixtures suitable for driving conventional combustion engines orhydrocarbons suitable for further industrial processing or othercommercial use. Intermediate products such as methanol or dimethylethermay also be generated by the production process of the invention. Theoverall process comprises in a preferred embodiment the conversion ofwater and carbon dioxide to C5+ hydrocarbons (i.e., with five or morecarbon atoms), preferably C5-C10 hydrocarbons. The overall process mayalso encompass the conversion of water and carbon dioxide to high cetanediesel or other liquid hydrocarbon mixtures suitable for drivingconventional diesel combustion engines.

Accordingly, the present invention provides in one aspect a process forproduction of liquid fuel from carbon dioxide and water usingelectricity, comprising:

-   -   providing water and electricity and electrolyzing the water into        hydrogen and oxygen,    -   providing carbon dioxide and reacting it with the obtained        hydrogen to produce methanol and/or carbon monoxide and water,    -   where said methanol can comprise the desired final product or be        reacted further to liquid hydrocarbon fuel, or,    -   in the case of carbon monoxide intermediate production, reacting        the obtained carbon monoxide with hydrogen in one or more steps        to produce liquid fuel, which can be methanol or other liquid        fuel such as liquid hydrocarbon fuel.

Thus, in one embodiment, the process comprises:

-   -   providing water and electricity and electrolyzing the water into        hydrogen and oxygen;    -   providing carbon dioxide and reacting it with the obtained        hydrogen to produce carbon monoxide and water; and    -   reacting the obtained carbon monoxide and hydrogen in one or        more steps to produce methanol or liquid hydrocarbon fuel        without intermediate methanol production, where said methanol        can optionally be processed further to liquid hydrocarbon fuel

Said carbon monoxide may be mixed with carbon dioxide for the furtherreactions to obtain liquid fuels.

Another aspect of the invention provides a process for production ofliquid fuel from carbon dioxide and water using electricity, comprising:

-   -   providing water and electricity and electrolyzing the water into        hydrogen and oxygen, and    -   providing carbon dioxide and reacting with the obtained hydrogen        to produce in a one step process liquid fuel.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic overview of a system according to the inventionillustrating all the main components: an electrolysis unit 4, a RWGSreactor 13, a methanol reactor 19, DME reactor 21 and gasoline reactor26.

FIG. 2 shows an alternative embodiment similar to the system of FIG. 1,except, in this case syngas is fed to a combined methanol/DME reactor32, coupled to the gasoline reactor.

FIG. 3 shows an embodiment with a Fisher-Tropsch type reactor 33, whichis fed with syngas and produces diesel.

FIG. 4 illustrates a bipolar alkaline electrolyzer system which isuseful for the system of the invention.

FIG. 5 shows in more detail one embodiment of a reverse water gas shift(RWSG) reactor system, which is part of the overall system of thepresent invention.

FIG. 6 shows a schematic overview of one type of methanol-to-gasoline(MTG) reactor system which forms part of the overall system of theinvention.

FIG. 7 illustrates a Fisher-Tropsch reactor used for the processdescribed herein.

DETAILED DESCRIPTION

Electrolysis of water to produce hydrogen and oxygen has been appliedfor a number of years on industrial scale and electrolytic hydrogenproduction systems are commercially available from a number of sources.Where water and electricity are available hydrogen production may,therefore, easily be installed. Hydrogen has been suggested as a futureenergy carrier replacing gasoline and diesel for fueling vehicles andships, at least in locations where renewable energy is abundant in orderto produce hydrogen by electrolysis or, as is more commonly used today,by steam reforming of natural gas (as a component of syngas, asmentioned above).

Electricity is an energy form that may be produced from alternative andrenewable energy sources such as geothermal sources, solar power, windenergy, hydro-power, and ocean thermal- or kinematic-power. It is alsoproduced in large quantities from nuclear power and may be producedthrough combustion of waste products (which would simultaneously produceCO₂). Electricity may also be made available through efficientutilization of off-peak power.

Carbon dioxide is generated in vast quantities in industrial processessuch as aluminum smelting, ammonia production, cement production, ironsmelting, ferro-alloy production, steel production, lime production,glass production and more, and also in large quantities from combustionprocesses such as in coal or gas power plants, vehicle operation andincineration or waste disposal. Carbon dioxide is also released inconsiderable quantities from geothermal power plants. Carbon dioxide istherefore available in close to unlimited quantities. Currenttechnologies to capture carbon dioxide from gas streams on a large scaleare mainly based on absorption on to amine based solvents. Such systems,like the CANSOLV® CO2 Capture System (Cansolv Technologies Inc.,Montreal, Canada) are commercially available and are operated in avariety of industrial processes. Other methods, based on physical orchemical solvents, membranes, solid sorbents, or cryogenic separation,have also been used to capture CO₂. What specific capture technology isthe most suitable depends on the process conditions under which it mustoperate. For the present invention, the skilled person can readily adoptany of the mentioned known techniques, depending on the specific sourceof CO₂ that is being utilized in each specific plant.

Depending on reaction conditions and catalyst selectivity, methanol caneither be produced directly from CO₂ and H₂ or via CO which is formed inthe competing reverse water gas shift reaction. The reverse water gasshift reaction has been shown to be a feasible method to convert carbondioxide to carbon monoxide with close to 100% equilibrium conversion.This opens up the possibility to produce high quality syngas of anydesirable composition from hydrogen and carbon dioxide.

From methanol, high octane gasoline may be produced over the dimethylether as intermediate. Likewise, high octane gasoline may also beproduced from syngas via the intermediates methanol and dimethyl ether.High cetane diesel and other hydrocarbons may also be produced directlyfrom syngas using the Fisher-Tropsch process or from methanol as theprimary feed.

Accordingly, it is highly advantageous to combine these processes in anefficient way to produce sulfur-free, high octane gasoline or highcetane diesel which can immediately replace the currently used gasolineand diesel distilled from petroleum oil without time-consuming technicaldevelopments and major infrastructural changes.

FIG. 1 shows a flow diagram for the overall process. Individual steps inthe process and variations thereof are detailed in the description ofpreferred embodiments. The overall chemistry and the energy balance ofthe process is shown in Formulas 1 through 8. The heat of reactions forformulas 1 through 7 is calculated from the corresponding heats offormation. For a (—CH₂—) unit the heat of formation is calculated as ⅛thof the heat of formation of octane. 1. 6H₂O (l) → 6H₂ (g) + 3O₂ (g)1.710 kJ Electrical energy 2. 2CO₂ (g) + 2H₂ (g) → 2CO (g) + 2H₂O (g)86.2 kJ Heat 3. 2CO (g) + 4H₂ (g) → 2CH₃OH (g) −181.6 kJ Heat 4. 2CH₃OH(g) → CH₃OCH₃ (g) + H₂O (g) −24 kJ Heat 5. CH₃OCH₃ (g) → 2(—CH²⁻) (g) +H₂O (g) −110 kJ Heat 6. 2CO₂ (g) + 2H₂ (g) → + 2O₂ (g) + 2(—CH₂—) (l)−229 kJ Heat balance 7. 4H₂O (g) → 4H₂O (l) −176 kJ Heat ofcondensation. 8. 2H₂O (l) + 2CO₂ (g) → + 3O₂ (g) + 2(—CH₂—) (l) 1305 kJEnergy balance

Formula 6 shows the balanced equation of all the reactions which occurafter the electrolysis step, i.e., steps 2-5, and the total amount ofgenerated heat is shown. Formula 7 shows the heat of condensation forthe produced water that is recycled in the process. The overall chemicalbalance for steps 1-5 and the calculated overall energy consumption ofthe process is shown in Formula 8.

The process starts with the conversion of water to hydrogen viaelectrolysis. Referring to FIG. 1, the water 1, led through pipe 112 ispurified before electrolysis in a purification/filtration unit 8 and maytherefore be of lower quality or where required, seawater may beutilized by using the appropriate purification methods. The purifiedwater is electrolyzed in an electrolysis unit 4 to form hydrogen 6 andoxygen 7 in a 2:1 molar ratio. The oxygen 7 is pressurized (compressor55 shown in FIG. 4 which illustrates further details of the electrolysisunit) and fed to storage tank 9, and will be partly utilized at a laterstage in the process for recycling 7′ of hydrocarbons not suitable forliquid fuels by partial oxidation or other processes described below.The hydrogen 6 is stored in an intermediate hydrogen storage tank 10after compression (compressor 54 shown in FIG. 4) to assure that theprocess can be run continuously where electrical power availabilityvaries, i.e., where electrical power is generated from solar or windenergy or where off-peak power is used.

The hydrogen 6 from the electrolysis unit 4 is transferred through line116 and mixed with carbon dioxide 1 collected from industrial emissionor other available sources, introduced through line 111 to produce aH₂:CO₂ mixture 11 of about 1:1 or any other mixture suitable for optimumperformance of the RWGS reactor 13 in step two or alternatives thereof.The carbon dioxide may be captured from mixed industrial gas streams,used directly after purification 5 from concentrated carbon dioxidestreams such as the emission from aluminum production or be from anyother economically utilizable carbon dioxide source.

In step two, the H₂:CO₂ mixture 11 of 1:1 or any other suitablecomposition is fed through a reverse water gas shift (RWGS) reactor 13converting the carbon dioxide and hydrogen mixture from tank 11 tocarbon monoxide and water 14 according to Formula 2. Excess heat fromother process steps is advantageously used to supply heat for thisendothermic part of the process.

In step three the carbon monoxide is mixed with hydrogen in a molarratio of H₂:CO of 2:1, or any other ratio most suitable for methanoland/or dimethylether production. The gas mixture in mixing tank 17 mayalso contain CO₂ and N₂ or any other component that facilitates theconversion to methanol or makes the overall process more efficient. Thegas mixture from tank 17 is fed through line 115 and compressor 18 to amethanol reactor 19 where the gas mixture is converted to methanol in ahighly exothermic process, according to Formula 3.

In step four the crude methanol water mixture is fed through line 20into a Methanol-to-Gasoline (MTG) reactor to be converted to high octanegasoline as described in the Mobil MTG process. The MTG reactor can be afluidized-bed MTG reactor or a fixed-bed MTG reactor or any alternativethereof. If a two stage fixed-bed reactor is used, the first stage 21where methanol is converted to DME may be decoupled from the secondstage 26 (as shown in FIG. 1) and DME may be drawn as an end productfrom the production process.

Alternatively, the process may proceed directly with a CO₂:H₂ mixture of1:3 or any other mixture suitable to produce methanol and/ordimethylether directly from CO₂ and H₂. The gas mixture in mixing tank17 contains in this alternative primarily CO₂ and H₂ but may alsocontain CO and N₂ or any other component that facilitates the conversionto methanol or makes the overall process more efficient. The gas mixturefrom tank 17 is fed through line 115 and compressor 18 to a methanolreactor 19 where the gas mixture is converted to methanol 20 in anexothermic process, according to: 9. CO₂ (g) + 3H₂ (g) → CH₃OH (g) + H₂O(g) −47.7 kJ Heat

In another alternative embodiment the process may proceed directly fromstep two to produce high cetane diesel or other hydrocarbon mixturessuitable to drive conventional combustion engines. In this case, asillustrated in FIG. 3, syngas 22 of suitable composition is fed directlyto a Fisher-Tropsch (“FT”) reactor 33 to preferably produce C10-C20hydrocarbons. In a simplified reaction scheme the FT process can bedescribed as follows:(2n+1)H₂+nCO→+CnH_(2n+2)+nH₂O   10.

The Fisher-Tropsch synthesis is a well developed process and a varietyof reactor designs have been implemented. In this embodiment the syngas22 is derived by mixing hydrogen from electrolysis of water with carbonmonoxide from the RWGS reaction of carbon dioxide which gives easy andunlimited control over the syngas composition. This has two advantageswith respect to the products from the FT reaction. Firstly, any desiredsyngas mixture may be produced as feed for the FT reactor, which allowsmuch better control of the final product composition. Secondly, the CO₂may easily be cleaned from sulfur containing compounds where necessary.The syngas so produced may therefore readily be obtained sulfur-free,leading to sulfur-free end product. Due to the flexibility in thecomposition of the syngas, the most preferred FT reactor type andsynthesis conditions may be any that lead to the most desirable productmixture and the highest conversion efficiency. This will partly dependon market demands.

Dimethyl ether 25 may also be produced directly from the syngas in steptwo without intermediate methanol production, as illustrated in FIG. 2.In that case a dehydration catalyst is mixed with the methanol synthesiscatalyst in a slurry type reactor 32. This promotes the production ofmethanol and its conversion to DME in the same reactor. Thereby methanolis continuously withdrawn from the syngas to methanol equilibriumreaction promoting the syngas conversion. The same applies for thedirect conversion of carbon dioxide and hydrogen to dimethyl ether.Dimethyl ether produced in this way may be utilized directly as fuel orfor further conversion to gasoline or diesel.

Lower grade components 28 such as LPG (liquefied petroleum gas, which isa mixture of butane and propane, also referred to as autogas), fuel gas(C1 and C2 hydrocarbons) and other hydrocarbons not suitable for highoctane fuel are preferably isolated and fed through line 28 (from theend product 27 which is directed through line 118 to storage tank 27)and are recycled. The recycling 29 is done by partial oxidation, steamreforming, autothermal reforming or by complete combustion. The productsof the recycling step depend on the recycling method and reactionconditions. They may be hydrogen, carbon monoxide, carbon dioxide, waterand heat. They will generally be fed appropriately back through line 30into the production line.

Water 14 produced in steps two, three and four, or the above describedalternatives thereof, may advantageously be collected by lines 114, 117and 124 and fed back through return line 31 to the electrolyzer unit 4.

Heat produced in the exothermic reactions in steps three through fivecan be suitably used to drive the endothermic process in step two (theRWGS process). The remaining heat can be utilized for mechanical worksuch as compression.

In one preferred embodiment of the process invention compression work isminimized by operating the electrolysis for H₂ and O₂ production at highpressure and either utilizing liquid, compressed or frozen CO₂ orcompressing CO₂ in multiple stages at as low a temperature as possibleby cooling between stages with cold sea water or other heat sink.

FIG. 1 illustrates several of the above alternative embodiments, Carbondioxide is fed from a source 1 through a purification unit 5(desulphurization and/or other purification means, as needed, dependingon the source and purity of carbon dioxide) through line 111 to mixingtank 11, generally after compression (not shown). A source of water 2 isfed through line 112 to a water purification unit 8, if needed, to anelectrolysis unit 4, run by electrical power 3. The electrolysis unit isdepicted in more detail in FIG. 4. The electrolysis unit 4 producesoxygen 7 and hydrogen 6, both of which would generally be compressed(compressors 54, 55 shown) and stored in intermediate storage tanks 9and 10. The CO₂ and H₂ mixture may if needed be further compressed (incompressor 16) before being fed to the RWGS reactor 13. The products ofwhich are shown as being separated in water 14 directed to line 114 andother products (CO and H₂ with residual CO₂) fed to syngas mixing tank17. Further separation of the products from the RWGS step is illustratedin further detail in FIG. 5 described below. The syngas directed throughline 115 is, if needed, compressed in compressor 18 before being fed toa methanol reactor 19 which produces methanol 20 fed to a DME reactor21. Alternatively, CO₂ and H₂ may be fed directly to the methanolreactor 19 loaded with a suitable catalyst or catalyst mixture toconvert CO₂ and H₂ directly to methanol. Independent of the productionroute, the produced methanol may be fed to a DME reactor 21 or directlythrough line 23 to the methanol-to-gasoline (MTG) reactor 26, which insuch case is configured applicably.

In another embodiment, reactor 21 can be a combined MeOH/DME reactorbeing fed directly with syngas or a suitable mixture of hydrogen andcarbon dioxide through line 22. The product from the final reactor isgenerally further separated and refined to provide the desired finalproduct 27, which can be gasoline of any desired grade. Undesiredhydrocarbons formed can be fed to oxidation unit 29 (various types asmentioned above), which is fed by oxygen 7′, which advantageously istaken from the oxygen 7 produced by the electrolysis. The oxidation unit29 is in some configurations further fed with CO₂ 1′, and returns aproduct mixture 30, which is shown here as being delivered to the syngasmixing tank 17 (optional intermediate purification and storage notshown).

FIG. 2 shows an alternative embodiment, using a reactor 32 (e.g. slurrytype reactor) comprising both dehydration catalyst and methanolsynthesis catalyst, which reactor is fed directly with syngas throughline 22. In this configuration dimethyl ether 25 is fed directly to thegasoline reactor 26.

FIG. 3 shows yet a further embodiment, with a Fisher-Tropsch typereactor 33 being fed with syngas 22 as discussed above.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The Overall Process

The overall process of the invention can be generally described as aprocess for producing liquid fuel and other hydrocarbon mixtures fromcarbon dioxide and water. The feedstock for the production iselectricity, industrial carbon dioxide and water. The end product can behigh octane gasoline, diesel or other liquid hydrocarbon mixturessuitable for driving conventional combustion engines. The end productcan also comprise other hydrocarbons for further industrial processingor commercial use, and the end product may additionally or alternativelycomprise dimethyl ether or methanol.

The overall process preferably comprises:

-   -   electrolytic production of hydrogen from water,    -   mixing of hydrogen to any desirable ratio with CO₂ to optimize        the conversion of CO₂ to CO via the RWGS reaction, or to any        ratio desirable to optimize methanol yield from a combined        RWGS-reaction with methanol synthesis or to any ratio desirable        to optimize direct methanol production from CO₂ and hydrogen;    -   mixing of hydrogen to any desirable ratio with CO to produce        syngas of optimal composition for any particular desired        purpose, such as for the conversion of premixed synthesis gas to        methanol, dimethyl ether or the direct conversion of the syngas        to hydrocarbon products;    -   synthesis of methanol directly from carbon dioxide and hydrogen        or alternatively from the produced syngas;    -   conversion of methanol to dimethyl ether (DME);    -   conversion of DME to high octane gasoline.    -   synthesis of high octane gasoline may also proceed directly from        crude methanol.    -   synthesis of high cetane diesel or other hydrocarbon mixtures        may also proceed directly from the produced syngas;    -   synthesis of dimethyl ether (DME) may also proceed directly prom        the produced syngas.

When hydrocarbon products such as high cetane diesel are produced, thepremixed syngas (comprising the electrolytically produced hydrogen, CO₂and the CO from the RWGS reaction of CO₂) is subjected directly to aFisher-Tropsch synthesis. The syngas mixture can be optimized tomaximize desired products yield.

Individual steps in the process are described in further detail below.

Step One: Electrolysis of Water to Produce Hydrogen

In the first step of the process, water 2 is electrolyzed in anelectrolysis unit 4 to form hydrogen 6 and oxygen 7, which are formed ina 2:1 molar ratio. The oxygen is pressurized in compressor 55 and fed tostorage tank 9 and will be partly utilized at a later stage in theprocess for recycling of hydrocarbons not suitable for liquid fuels bypartial oxidation or other processes described herein. The excess oxygenis a valuable side product for industrial or commercial use. Thehydrogen from the electrolyzer unit is typically compressed bycompressor 54 and stored in an intermediate hydrogen storage tank 10 toassure that the process can be run continuously where electrical poweravailability varies, i.e., where electrical power is generated fromsolar or wind energy or where off-peak power is used.

The reaction is conveniently performed with state of the art BipolarAlkaline Electrolyzer (BAE) units, or any other electrolyzer unitsequivalent or superior to the BAE units in production capacity andenergy efficiency.

FIG. 4 shows a process flow diagram for hydrogen production based on theuse of a BAE unit. The total efficiency of the electrolyzer unit israised by about 10-15% by using excess energy from the recycling ofhydrocarbons not suitable for use as liquid fuel, e.g. LPG, light fuelgas and higher hydrocarbons and/or by using excess energy fromexothermic steps in the production process for compression of the gasesand other energy demanding utilities. The figure shows a compressor 54for compressing the generated hydrogen 6 and a compressor 55 forcompressing the oxygen 7, both gases are conveniently stored inintermediate storage tanks, 9 (oxygen) and 10 (hydrogen). The water isobtained from any applicable source 2 and may optionally if needed bepurified in a filtration unit 50. Water 14 produced from subsequentsteps in the overall process may optionally be recycled forelectrolysis. An electrolyte (KOH) source 52 is also shown as well as anelectric power source 3. Some of the required electricity can begenerated from the heat which forms in subsequent exothermic steps inthe overall process. The electrolysis rector 53 includes theelectrolysis module itself, electrolyte circulation and hydrogen gasdrying and purification means.

Step Two: Conversion of Carbon Dioxide to Carbon Monoxide

The hydrogen 6 obtained in step one is mixed with carbon dioxide 1 fromindustrial emission to produce a H₂:CO₂ mixture 11 preferably of a ratioof 1:1, however, any other mixture ratio may as well be used, which issuitable for optimum performance of a Reverse Water Gas Shift Reactor oralternatives thereof.

Conversion of carbon dioxide via the reverse Water Gas Shift Reaction(RWGSR):CO₂(g)+H₂(g)→CO(g)+H₂O(g) ΔH=43.1 kJ/mol

The mixture of H₂ and CO₂ is fed through a Reverse Water Gas Shift(RWGS) Reactor 13 charged with about 10w % Cu loaded g-alumina catalystand/or other suitable catalysts to convert the carbon dioxide to carbonmonoxide. The catalyst may be a commercially available CuO, ZnO and/orAl₂O₃ based catalyst but is not limited to those. The reactor is eitherrun in recycling mode, with close to 100% equilibrium conversion, oralternatively conditions can be arranged to drive the reaction tocomplete consumption of one of the reactants by overload of the otherand removal of products, preferably water. The water 14 from the exhaustis condensed and advantageously fed back through line 31 to theelectrolyzer unit 4 and the carbon dioxide may be separated byisothermal compression and further cooling or by other suitable methods.The carbon dioxide is then fed back through 15 to the RWGS reactor 13.The remaining carbon monoxide and hydrogen may be fed directly to thesyngas blender 17 or alternatively the hydrogen may be partly or fullyseparated from the gas mixture by membrane filtration and fed back tothe RWGS reactor. Excess heat from other process steps is advantageouslyused to supply heat for this endothermic part of the process.

In an alternative embodiment, a suitable amount of CO₂ is provided toobtain a H₂:CO₂ reactant mixture of about 2:7 ratio, to which is mixedabout 10% of a suitable buffer gas (e.g. Argon). Such mixture is fedthrough a Reverse Water Gas Shift Reactor loaded with about 5 wt %Cu/silica catalyst or other suitable catalysts to convert the carbondioxide in to methanol and carbon monoxide, preferably with highmethanol selectivity.

The methanol and the water formed in the reaction are separated from theexhaust by condensation and the carbon dioxide is separated from theremaining gases and fed back to the RWGS reagent gas blender. Carbonmonoxide produced and remaining hydrogen is fed to the syngas blender.

With a suitable catalyst and by optimizing the reaction conditions i.e.,the reactant ratio, the pressure and the space velocity, the productratio of carbon monoxide to methanol can be optimized to an extent wherethe exothermic methanol synthesis supplies sufficient heat to run themildly endothermic carbon monoxide production.

FIG. 5 illustrates a preferred embodiment of the RWGS step. CO₂ from anapplicable source 1 is typically compressed by a compressor 78 beforebeing fed to a CO₂:H₂ mixing unit, into which H₂ 6 formed in theelectrolysis 4 is fed from an intermediate storage tank 10, optionallythrough a compressor 79, or the hydrogen may be stored under sufficientpressure. The CO₂ H₂ mix is fed to the RWGS reactor 13, the products ofwhich are fed to a condenser, separating out produced water 14. The heatgenerated by condenser 61 is shown being supplied back to the reactor todrive the endothermic reaction. The products 73 are further fed to amembrane filtration unit 62 (in this case valve 63 is open and valve 66is closed) to separate out hydrogen (to tank 69, from which the hydrogencan be recycled to the CO₂:H₂ blender), the thus obtained CO:CO₂ mixtureis directed through line 74 to a condenser 64 for separating out CO₂which can be fed through line 76 back to the mixing tank 11 and the COis shown fed to tank 11. The arrangement shown with valves 63 and 66 isto illustrate that the order of the separation can be reversed (valve 66open and 63 closed), first condensing out the CO₂ and subsequentlyremoving H₂.

Step 3: Methanol Production from Hydrogen and Carbon Monoxide

In step three the carbon monoxide is mixed with hydrogen in a molarratio of H₂:CO of 2:1 and fed through a methanol reactor. The reactor ispreferably a Liquid phase methanol reactor based on inert hydrocarbonmedia and conventional copper-zinc catalyst, such as described e.g. inU.S. Pat. No. 4,910,227. The methanol reactor may also be a multistageadiabatic reactor or a cooled tubular reactor as currently used inindustrial methanol production. The methanol synthesis may also becarried out in the presence of a water-soluble basic substance wherewater is used as slurry medium, as disclosed in Japanese Patent No.57126434 or with any other suitable slurry media or reactor type. Themethanol thus formed can be pooled with methanol/water obtained in step2, if methanol is being directly produced in step 2 as described above.The remaining gas reenters the reactor.

The methanol formation is a strongly exothermic process, which makes itdifficult in practice to maintain constant and uniform temperature inisothermal reactors such as a tubular reactor. This may, however, becontrolled to a large extent by controlling the composition of thesyngas. As described above for step two, preferred embodiments allowcomplete control of the syngas composition. This is used to maximize theutilization of excess heat from this highly exothermic reaction and tomaintain maximal control of the thermal conditions of the reactor. Forexample; the heat release may be increased by adding excess CO but maybe reduced by adding a small amount of CO₂. Through better heat controlbyproducts such as higher alcohols, esters and ketones are minimized andthe lifetime of the catalyst extended.

Alternative Embodiment: Direct Methanol Production from Carbon Dioxideand Hydrogen

Carbon dioxide is reacted with hydrogen to produce methanol directly,that is, without a distinctly separate RWGS reaction step. Hydrogenreacts with carbon dioxide in a 3:1 ratio or any other desirable ratiosto produce methanol and water in a 1:1 ratio. Hydrogen from electrolysisand carbon dioxide from emissions capture are here directly reacted overa Cu/ZnO/Al₂O₃, Cu/ZrO₂ or a CU—Zn—Cr based catalyst or any othercatalyst suitable for the conversion of carbon dioxide and hydrogen toproduce methanol and water.

A reactant circulation loop containing carbon dioxide and hydrogencarries a reactant mixture through a catalyst containing reactor, acounter-flow heat exchanger, a condenser, and a circulation pump. Thereactant mixture prior to entering the reactor passes through thecounterflow heat exchanger as the exiting reactant mixture passesthrough the counterflow heat exchanger in the opposing direction.

As the reactant mixture passes through the reactor, hydrogen and carbondioxide react, forming methanol and water. The mixture approaches anequilibrium composition with 20 to 25% of the reactant mixture beingconverted to methanol and water. The methanol and water formed iscondensed as it passes through the condenser. After passing through thecirculation pump, additional carbon dioxide and hydrogen are added toreplace that which has reacted to methanol and water.

The pressure in the loop is nominally about 50 bar and the temperatureof the reactor is about 225° C. Methanol and water are condensed out ofthe loop by operating the condenser at 20° C.

Step Four: Methanol to Gasoline Process

In step four the crude methanol and water mixture from the directconversion of carbon dioxide and hydrogen to methanol or methanol andwater from the combined steps two and three is fed into a Methanol toGasoline (MTG) reactor to be converted to high octane gasoline in theC5-C10 range. A suitable embodiment of this process, referred to as theMobil MTG process, is described in detail in U.S. Pat. Nos. 4,788,369,and 4,418,236. The process is originally described for a fixed-bedreactor but has also been developed for fluidized-bed reactors. Thefixed-bed arrangement has been used in large industrial scale reactorsused in the New Zealand GTG plants and the liquid-bed reactors have beendemonstrated on commercial scale. The conversion of methanol to highoctane fuel in this embodiment may be carried out in a fixed- or afluidized bed Mobil MTG reactor but is not limited those particularreactor types. The advantage of the fluidized bed is the better heatcontrol and the close to 100% conversion efficiency in one run. Theadvantage of the fixed-bed reactors is the extensive experience in theiroperation and that the methanol to gasoline synthesis runs in two stepswhere dimethyl ether may be withdrawn from the first step as finalproduct.

FIG. 6 illustrates one embodiment of a useful setup for gasolinesynthesis. Methanol (or alternatively dimethylether or a mixturethereof, depending on the configuration and catalyst composition of thereactor) is fed through in-feed line 85 to reactor 86 which deliversproducts to separator 88 and excess heat 97, which can advantageously beutilized elsewhere in the overall process as described herein. Theseparator separates out light weight hydrocarbons which are fed to arecycling oxidation unit 93, which can be set up to produce CO and/orCO″, some of which may be fed back to reactor 86 or other precursor stepin the overall process. Water is separated to storage 14, otherhydrocarbon products are fed to further separation/refining to obtainthe desired final gasoline product 27 and other hydrocarbon products 95may be separated as well for further use and/or as a separate commodity.

Alternative to Step Three and Four: Syngas to Diesel or OtherHydrocarbon Mixtures Suitable to Drive Combustion Engines

In an alternative embodiment, synthesis of high cetane diesel or otherhydrocarbon mixtures may proceed directly from the syngas produced byelectrolyzes of water and the RWGS reaction of the produced hydrogenwith carbon dioxide. In this embodiment a suitable CO:H₂ mixture, whichmay also be blended with other gas components such as CO₂ or buffer gas,is fed directly to a Fisher-Tropsch reactor. A suitable embodiment ofthis process is a reactor type which is in based on the reactor designpublished in the article Fisher-Tropsch synthesis in Slurry Phase by M.D. Schliesinger et al. in Engineering and Process Development, vol.43(6), 1474 (1951). A suitable adaptation of this reactor type isdescribed in detail in U.S. Pat. No. 5,500,449. This adoption describesa slurry reactor which is loaded with a suitable catalyst and istypically operated around 250° C. and at 300 psia. However,

Due to the flexibility in the composition of the syngas, the mostpreferred FT reactor type and syntheses conditions may be any that leadto the most desirable product mixture and the highest conversionefficiency.

FIG. 7 shows a schematic setup of a Fisher-Tropsch type reactorarrangement, with an appropriate CO:H₂ mixture 22 being fed to reactor101, the products of which are fed to separator 103 for furtherseparation. The separator delivers water fed through 89 to storage 14,lighter hydrocarbons which are recycled to oxidation 93; CO from theoxidation recycling is fed back through 96 to reactor. Main hydrocarbonfraction 104 is fed to further refining/fractionation 106. High cetanediesel is fed through 107 to tank 39 and other products 108 which are aswell of commercial value are separated and collected.

Recycling of Lower Grade Components Such as LPG, Fuel Gas and OtherHydrocarbons Not Suitable for Liquid Fuel

In liquid fuel production from methanol or syngas, LPG and fuel gas mayamount to 15%-40% of the product by weight depending on reactor type andreaction conditions. Those and other minor components are not suitablefor liquid fuel or for further industrial processing or commercial use.To increase the efficiency of the overall process about 15-40%, allhydrocarbons not suitable for high octane fuel are recycled for furtherindustrial processing or commercial use. The recycling may proceedthrough one of the following processes.

-   -   i) Through partial oxidation with pure oxygen from the        electrolyzer unit in a partial oxidation reactor POX. The carbon        monoxide hydrogen mixture formed is then blended with the        premixed synthesis gas and fed to the liquid methanol reactor as        described in step three. Carbon dioxide may also be blended to        the POX reactor feed, resulting in additional CO output.    -   ii) Through steam reforming, whereby the hydrocarbon feed is        blended with one to two carbon equivalent of CO₂ and about one        to two hydrocarbon carbon equivalent of water steam. Depending        on the CO to CO₂ ratio, the gas mixture resulting from the steam        reforming process is fed directly to the syngas blender or RWGS        reactant blender after condensation of the water steam, where        advantageously, the gas mixture may be separated and fed back to        the process as appropriate. Water is recycled in to the        electrolyser unit.    -   iii) Through autothermal reforming, combining the partial        oxidation process with steam reforming. This has the advantage        that the heat from the exothermic partial oxidation helps        driving the endothermic steam reforming process. Advantageously        the pure oxygen for this process is delivered from the        electrolyzer unit. After condensation of the water products gas        mixture may be fed directly to the syngas mixer, or the RWGS        reactant blender depending on the CO:CO₂ ratio. The gas mixture        formed may also be separated and fed back to the process as        appropriate. Water is recycled in to the process.    -   iv) Through total oxidation, whereby the hydrocarbons not        suitable for liquid fuel are burned with excess oxygen in a        suitable heat exchanger to maximize exploitation of the heat        released in this highly exothermic reaction. Advantageously the        hydrocarbons are burned with pure oxygen from the electrolyzer        unit. Water is separated from the carbon dioxide produced and        feed back to the electrolyzer unit. The carbon dioxide formed is        feed to the blender for the RWGS reactor. Heat released in the        reaction is utilized in other process steps, such as        compression, preheating of reactant streams, preferably the        reactant stream for the RWGS reaction, or to drive endothermic        reactions in this process.

Independent of the method used for recycling of lower grade componentssuch as LPG, fuel gas the heat take out of the product gas mixture isused for compression, preheating of reactant streams, or to driveendothermic reactions in this process.

EXAMPLES

Herein below are described specific suitable arrangements and conditionsfor performing the process of the invention. These examples should notbe considered as limiting the overall scope of the invention.

Example 1 Hydrogen Production Using a BAE-Unit of 2328 kW

Production capacity is 43.6 kgH₂/hr with an conversion efficiency of 80%(water to hydrogen) and an overall energy efficiency of 73% when thecompression of hydrogen and oxygen is included.

The energy efficiency, which is calculated as the higher heating valueHHV of hydrogen divided by the electrical energy consumed to produce onekg of hydrogen can advantageously be raised to about 83%.

This is done by utilizing excess energy from recycling of fuel gas, LPGand other hydrocarbons not suitable for liquid fuel and/or by usingsteam generated in the heat exchangers used to balance the highlyexothermic methanol production, the MTG or the FT reaction forcompression of the gases.

Example 2 Conversion of H2 and CO2 to Methanol in a Reaction Loop

H₂ and CO₂ are supplied at 50 bar pressure and molar ratio of 3:1 (H₂ toCO₂) to a methanol synth reactor loaded with a Cu/ZnO/Al₂O₃, Cu/ZrO₂ ora CU—Zn—Cr based catalyst, or any other catalyst suitable for theconversion of carbon dioxide and hydrogen to produce methanol and water.

The reactor is operated at 225° C. and 20% of the input stream reacts tomethanol and water in an equal molar ratio. After exiting the reactor,the output stream is cooled by counterflow heat exchange with the inputstream. Then the output stream is further cooled so as to condense thereaction products (water and methanol). The condensed products arecollected and periodically ejected, while the non-condensed gases arerecirculated by a circulation pump and combined with new incoming inputstream.

Example 3 Conversion of CO₂ to CO in an RWGS Reactor

The RWGS reaction is carried out in a fixed bed tubular reactor chargedwith 10 w % Cu loaded g-alumina catalyst. The feed is a 1:1 mixture ofCO₂ and H₂ at 400° C. and 5 bar. It has been shown, that under thoseconditions higher than 95% equilibrium conversion may be achieved on aroutine basis. At 400° C. the equilibrium constant for the reaction isabout 0.08 which translates to about 27% CO/CO₂ ratio at 95% equilibriumconversion.

The conversion can be run in recycling mode, where exhaust water iscondensed and fed back to the electrolyzer unit and the carbon dioxidemay be separated by isothermal compression and further cooling or byother suitable methods. The carbon dioxide is then fed back to the RWGSreactor. The remaining carbon monoxide and hydrogen may be fed directlyto the syngas blender or alternately the hydrogen may be partly or fullyseparated from the gas mixture by membrane filtration and fed back tothe RWGS reactor. The excess heat removed from the exhaust gas and theheat of condensation from the water is fed back to the RWGS reactorthrough a counter flow heat exchanger.

The conversion may also be driven to complete consumption of H₂ by usingan overload of CO₂ which is recycled and fed back to the reactor and/orby removing the water from the reactor by using desiccant beads or acondensing apparatus. Just the same, the reaction may be driven tocomplete CO₂ consumption by excess hydrogen and/or water removal. Inthat case the remaining exhaust water is removed by condensation and theexcess hydrogen is separated from the exhaust through hydrogen permeablemembrane filtration and feed back to the reactor.

Example 4 Conversion of CO₂ to CO at High Pressure to ProduceStoichiometric Syngas for Direct Fed to the Methanol Reactor

With either excess H₂ or excess CO₂ it is possible to produce a syngassuitable for direct synthesis of crude methanol having the desiredcomposition for subsequent conversion to gasoline or other liquid fuel.

In this example the RWGS reaction is carried out at 50 bar and 500° C.with a 10w % Cu loaded g-alumina catalyst. The catalyst may also be acommercially available CuO, ZnO and/or Al₂O₃ based catalyst but is notlimited to those. In this example, where the produced syngas is intendedas feed for a methanol reactor the preferred reactant ratio in the feedgas stream 2:1 (H₂:CO₂). A part of the CO₂ in the feed mixture isrecycled from the reactor exhaust.

The high pressure chosen in this example has two main advantages.

Firstly, the high pressure is compatible with the requirement forremoval of excess CO₂ by condensation. All utilizable heat may bewithdrawn from the reactors exhaust as the water is condensed by coolingthe exhaust to any suitable temperature lower than 265° C. CO₂ iscondensed in a second step by cooling of the gas stream further, i.e.,below 13° C. This may be done by transferring the waste heat to coldseawater or other suitable heat sink. Where a heat pump or refrigerationunit is necessary for this second step to reach the end temperaturedesired, the minimal temperature difference between hot and cold sidesof the heat pump assures for optimal performance.

Secondly, after removal of water and CO₂ at 50 bar pressure, the RWGSreactor can feed directly into a methanol synthesis reactor of standardtype, without additional compression. Compression can therefore becarried out on the H₂ and CO₂ feedstock at the lowest possibletemperature to minimize energy required. At that point, prior to theRWGS reactor, H₂ and CO₂ feed streams can be cooled with availableresources, such as cold seawater, for maximum compression efficiency.Multistage compression with intercooling between stages can approximateiso-thermal compression for maximum efficiency.

The higher temperature increases the equilibrium constant from about0.08 at 400° to about 0.14 at 500° C. and thereby shifts the reactionequilibrium advantageously toward more CO formation.

Under those conditions the preferred reactant mixture of H₂ to CO₂ of2:1 leads to the production of a stoichiometric syngas mixture that canbe feed directly to the methanol reactor as described in step 3 aboveand example 4 below.

In this embodiment the H₂:CO₂ ratio may be tuned in any such way as tooptimize the syngas mixture for its intended use, independent if it isintended as feed for a methanol reactor, dimethyl ether reactor, aFisher-Tropsch reactor or any other reactor type advantageous for thedisclosed process.

Example 5 Methanol Production in a Slurry Bubble Reactor

Methanol is produced in a slurry bubble reactor of LPMEOH™ type, such asare described in detail in Department of Energy/National EnergyTechnology Laboratory Report no. DOE/NETL-2004/1199 and U.S. Pat. No.4,910,227. Typically, a syngas composition of about 60% CO, 25% H₂, 9%CO₂, and 4% N₂ enters the slurry reactor from the bottom. The feedstream is preheated to about 205° C. (400° F.) before entering theslurry bubble reactor which contains a slurry comprising in the range of25-45 wt % BASF S3-85 catalyst or other suitable catalyst to convertsyngas to methanol. The reactor is typically operated at about 725 psiand in the range of 200-290° C. (400-550° F.) at a gas hourly spacevelocity (GHSV) in the range of 5.000-10.000 standard liter/kgcatalyst-hr. The methanol steam and remaining reactant gas disengagesfrom the slurry and gathers in the slurry free zone at the top of thereactor from where it is collected. The exit gas is cooled in two steps.In the first step, vaporized oil from the slurry is condensed andbrought back to the reactor, and in the second step the methanol/watervapor is condensed and the remaining syngas which still contains somemineral oil from the slurry and some minor amount of methanol is fedback to the feed stream. In this example the heat of the reaction isremoved by steam generation in a cooling coil inundated in the slurry inthe reactor. The superheated steam can be used for preheating chemicalstreams, compression of gases, driving of the endothermic RWGS reactionor for additional electricity production.

Example 6 Conversion of Crude Methanol to Gasoline in a Fluidized-BedCatalyst Process

The crude methanol which typically contains about 83% methanol and 17%water is injected as liquid or as superheated vapor at 413° C. in to adense fluidized-bed catalyst reactor loaded with a ZSM-5 type catalystor other suitable catalyst for the conversion of methanol to gasoline. Aquantitative conversion is achieved in one pass at typical reactionconditions of 40-60 psia and 380-403° C. with in the range of 500-1050kg/hr methanol feed rate. The heat from the highly exothermic reactionis removed by steam generation in a cooling coil inundated in the slurryin the reactor. The superheated steam can be used for preheatingchemical streams, compression of gases, driving of the endothermic RWGSreaction or for additional electricity production. After catalystdisengagement the product vapor is condensed, and the gasoline separatedfrom the water. Fuel gas, LPG and other components not suitable for highoctane gasoline are preferably separated from the gasoline fraction andfed to a partial oxidation reactor.

Example 7 Conversion of Crude Methanol to Gasoline in a Fixed-BedCatalyst Process

In the fixed-bead MTG reactor the crude or dried methanol first enters aDME reactor where methanol undergoes a dehydration reaction in contactwith an alumina catalyst at 300-420° C., to form an equilibrium mixtureof methanol, water and dimethyl ether. The effluent from the DME reactorenters in a second stage a fixed-bed reactor loaded with Zeolite ZSM-5catalyst where it is converted to gasoline products at 360-415° C. and315 psig. The excess reagents from the second stage of this fixed beadMTG process are recycled by recombining them with the effluent from thefirst stage i.e. the DME reactor. The second stage is typically run withmultiple reactors where one is always in regeneration mode.

The first stage in the fixed bed MTG process may be decoupled from thesecond stage to draw DME as an end product from the production process.In such case the reaction would be driven beyond equilibrium efficiencyby removal of DME and water through evaporation of the DME and orcondensation or desiccation to remove water.

Example 8 Production of Liquid Fuel Such as High Cetane Diesel ViaFischer-Tropsch Synthesis

The Fisher-Tropsch (FT) synthesis is conducted in a slurry phase reactorwhere an iron catalyst is suspended in inert hydrocarbon media. Thereactor is charged with inert hydrocarbon slurry with 5% -15% ironcatalyst by weight with particle size ranging from 5 μm (micrometer) to40 μm. The percentage of alkali metal and copper in the catalyst may bechosen to promote desired end products, but is preferably in the rangeof 0.005 to 0.015 and in the range of 0.005 to 0.050, respectively.Other catalysts that promote the FT synthesis in a desirable way mayalso be used. The operating pressure of the reactor is within the rangefrom 100 psia to 500 psia and operating temperatures are in the rangefrom 220° C. to 280° C. The preferred space velocity is between 100 and300 cubic feet per hour per cubic feet of expanded catalyst bead. Inthis embodiment the most preferable reaction conditions for the FTsynthesis are optimized to maximize the C10 to C20 fraction of theproduct for utilization as high cetane diesel. The heavier waxes areseparated from the catalyst bed using a cross-flow filter and returningthe catalyst to the reactor. The lighter hydrocarbons are separated by acold trap or by distillation and fed directly to the hydrocarbonrecycling unit which may be a POX reactor or another alternative asdescribed above. The waxes can be converted to additional liquid fuel(Disel and Naphtha) by thermo cracking at 410° C. In this example theheat of the FT reaction is removed by steam generation in a cooling coilinundated in the slurry in the reactor. The superheated steam can beused for preheating chemical streams, compression of gases, driving ofthe endothermic RWGS reaction or for additional electricity production.

Example 9 Recycling of Hydrocarbons Not Suitable for High Octane Fuel byCatalytic Partial Oxidation and Use of Pure Oxygen from the ElectrolyzerUnit

a) Through Partial Oxidation of Fuel Gas and LPG

The fuel gas and LPG fraction from the MTG or the FT synthesis may berecycled by none-catalytic or catalytic partial oxidation.

In none-catalytic partial oxidation a burner is fed a mixture of oxygenand hydrocarbons containing about 0.45 carbon equivalent of pure oxygenfrom the electrolyses process described in step one and example 1.

The gas mixture is brought to ignition temperature by an external sourceand the gas feed is adjusted to optimize performance. As the ignitionmay require higher oxygen content than optimal for the POX reaction andtherefore different burner design, the ignition may be assisted by acatalyst.

The partial oxidation may also be carried out using a catalyst asdescribed in a number of patent documents, e.g., U.S. Pat. No.4,844,837; U.S. Pat. No. 4,087,259, U.S. Pat. No. 5,648,582 and U.S.Pat. No. 6,254,807. In one example of the catalytic POX reaction anoxygen/hydrocarbon mixture containing 0.4-0.6 carbon equivalent ofoxygen is preheated to about 200° C. The oxygen/hydrocarbon mixture isfed to a POX reactor with a monolith catalyst that has been preheatedwith an external source to a temperature close to the ignitiontemperature. After ignition a monolith catalyst temperature of near1000° C. is established and no further external energy is required.

Independent of the POX reactor type, carbon dioxide may be mixed to theoxygen/hydrocarbon feed to reduce formation of elemental carbon and toincrease the CO production.

The product gas is cooled in a suitable heat exchanger to utilize theexcess heat for compression or other energy demanding steps in theprocess. If the syngas is intended for synthesis, such as the methanolsynthesis, where the syngas is preheated, it is preferable to retain theappropriate portion of the excess heat in the product, wherein the hotproduct gas enters preferably directly the syngas blender, where it isbalanced.

b) Through Steam Reforming of Fuel Gas and LPG.

In this example steam reforming is conducted substantially as describedin U.S. Pat. No. 5,500,449. The gas stream containing the lighterhydrocarbons is mixed with one to two carbon equivalent of carbondioxide to prevent elemental carbon production. The carbon dioxide andhydrocarbon gas mixture is then mixed with steam to produce a mixturecontaining about 1 mol carbon from hydrocarbons to 1-2 mole water.Preferably the steam needed for the steam reforming is branched of thesuperheated water steam from the heat exchanger in the methanol-, MTG-or FT-reactor. The preheated gas/steam mixture enters a conventionalsteam reforming reactor charged with commercially available Nicelcatalyst. The conversion of the hydrocarbons to carbon monoxide andhydrogen takes place at 700° C.-900° C. at a system pressure that may bebetween 12 and 500 psia. A typical flow rate for such reactor would beabout 300 lbs/hr/cubic feet of catalyst. After condensation of the waterthe product gas from the steam reforming may be fed directly to thesyngas mixer or may be freed from carbon dioxide and other minorcomponents first, depending on the intended application of the syngas.

1. A process for production of liquid fuel from carbon dioxide and waterusing electricity, comprising: (a) providing water and electricity andelectrolyzing the water into hydrogen and oxygen; (b) providing carbondioxide and reacting with the obtained hydrogen to produce methanoland/or carbon monoxide and water; and (c) reacting the obtained methanoland/or carbon monoxide mixed with hydrogen in one or more steps toobtain liquid fuel, or providing said methanol as the desired liquidfuel.
 2. The process of claim 1, wherein in step (b) methanol isproduced directly from said carbon dioxide and hydrogen.
 3. The processof claim 1, wherein in step (b) carbon monoxide and water is obtained,and in step (c) the obtained carbon monoxide is mixed with hydrogen fromstep (a) to produce in one or more steps liquid fuel.
 4. The process ofclaim 1, wherein in step (c) said carbon monoxide is mixed with carbondioxide and hydrogen to produce liquid fuel.
 5. The process of claim 1,further comprising the steps of: (d) separating hydrocarbon byproductsfrom desired liquid fuel product(s); (e) reacting the separatedhydrocarbon byproducts to produce carbon monoxide and/or carbon dioxide,hydrogen and water; and (f) introducing said carbon monoxide and/orcarbon dioxide and hydrogen produced in step (e) to the reaction(s) ofstep(s) (b) and/or (c) to produce liquid fuel.
 6. The process of claim5, wherein said separated hydrocarbon byproducts are reacted with oxygenin a partial oxidation process to produce carbon monoxide and hydrogen,which are recycled as reactants in preceding reactions in the process.7. The process of claim 5, wherein said separated hydrocarbon byproductsare reacted with oxygen in an autothermal process to produce carbonmonoxide and hydrogen, which are recycled as reactants in precedingreactions in the process.
 8. The process of claim 5, wherein saidseparated hydrocarbon byproducts are reacted with oxygen in a steamreforming process to produce carbon monoxide and/or carbon dioxide andhydrogen, which are recycled as reactants in preceding reactions in theprocess.
 9. The process of claim 5, wherein said separated hydrocarbonbyproducts are reacted with oxygen in an autothermal process to producecarbon dioxide and hydrogen, which are recycled as reactants inpreceding reactions in the process.
 10. The process of claim 5, whereinsaid separated hydrocarbon byproducts are reacted with oxygen in antotal oxidation process to produce carbon dioxide and hydrogen, whichare recycled as reactants in preceding reactions in the process.
 11. Theprocess of claim 1, further comprising the steps of: (d) separatinghydrocarbon byproducts from desired fuel product(s); (e) reacting theseparated hydrocarbon byproducts with oxygen in a total oxidationprocess to produce carbon dioxide, and water; and (f) introducing thecarbon dioxide produced in said oxidation process in step (e) to thereaction of step (b) to produce carbon monoxide. (g) introducing thewater produced in said oxidation process in step (e) to the reaction ofstep (a) to produce hydrogen.
 12. The process of claim 5, where carbondioxide is added to the reactants in step (e).
 13. The process of claim1, where heat from the liquid fuel synthesis in step (c) is utilized todrive the production of carbon monoxide and water in step (b).
 14. Theprocess of claim 1, where the liquid fuel synthesis in step (c)comprises the production of dimethyl ether.
 15. The process of claim 1,where the liquid fuel synthesis in step (c) comprises the production ofmethanol.
 16. The process of claim 1, where the liquid fuel synthesis instep (c) comprises the production of gasoline.
 17. The process of claim1, where the liquid fuel synthesis in step (c) comprises the productionof diesel.
 18. A process for production of liquid fuel from carbondioxide and water using electricity, comprising: (a) providing water andelectricity and electrolyzing the water into hydrogen and oxygen, and(b) providing carbon dioxide and reacting with the obtained hydrogen toproduce in a one step process liquid fuel.
 19. The process of claim 18,wherein said produced liquid fuel comprises methanol.
 20. The process ofclaim 18, wherein said produced liquid fuel comprises liquid hydrocarbonfuel.
 21. The process of claim 1, where liquid fuel is produced fromhydrogen and carbon dioxide, said carbon dioxide captured directly fromlocalised emissions from an industrial plant and/or power plant.
 22. Theprocess of claim 21, where said industrial plant and/or power plant isselected from the group consisting of a geothermal power plant, analuminium plant, a coal fired power plant and a cement production plant.23. The process of claim 14, where the liquid fuel synthesis in step (c)comprises a two-step process of (i) producing DME, and (ii) producinggasoline.
 24. The process of claim 14, where the liquid fuel synthesisin step (c) comprises a two-step process of (i) producing DME, and (ii)producing diesel.
 25. The process of claim 15, where the liquid fuelsynthesis in step (c) comprises at least three sub-steps comprising (i)producing methanol, (ii) producing DME, and (iii) producing gasoline.26. The process of claim 15, where the fuel synthesis in step (c)comprises at least three sub-steps comprising (i) producing methanol,(ii) producing DME, and (iii) producing diesel.
 27. The process of claim1, where the liquid fuel synthesis in step (c) comprises a one-stepFisher-Tropsch type process for producing liquid hydrocarbons includinggasoline and/or diesel.
 28. The process of claim 5, wherein saidhydrocarbon byproducts comprise one or more of the components selectedfrom unsaturated and saturated, linear and branched C1-C4 hydocarbonsincluding methane, ethane, ethene, ethyne, butane, butene, tert-butane,propane and isobutane.
 29. The process of claim 1, wherein thecomposition of the reactant mixture is optimized to maximize desiredproducts yield.
 30. The process of claim 5, where the total electricalenergy consumption of the electrolysis unit is lowered by using excessenergy from said recycling of hydrocarbons not suitable for use asliquid fuel and/or by using excess energy from exothermic steps in theproduction process.
 31. The process of claim 1, where the totalelectrical energy consumption of the electrolysis unit is lowered byusing heat energy generated in other step(s) of the process forcompression of the electrolysis products.
 32. The process of claim 1,where the total electrical energy consumption of the electrolysis unitis lowered by using heat energy generated in other step(s) of theprocess converted to electric energy to supply electric power to theelectrolysis.
 33. The process of claim 1, where the product ratio ofcarbon monoxide to methanol is optimized to an extent where theexothermic methanol synthesis supplies most or all of the required heatto run the mildly endothermic carbon monoxide production.
 34. Theprocess of claim 1, where the generation of heat in step (c) iscontrolled by increasing the relative amount of CO to increase heatand/or by adding CO₂ to decrease generated heat.
 35. The process ofclaim 34, wherein product ratio, including methanol formation, iscontrolled by adjusting composition of syngas reactants carbon monoxideand hydrogen in step (b) and/or (c).
 36. The process of claim 1, whereingenerated heat in the process is used for compression, preheating ofreactant streams, or to drive endothermic reactions in the process. 37.The process of claim 1, wherein work required for compression is reducedby utilizing CO₂ provided in pressurized, liquefied or frozen condition.38. The process of claim 1, wherein work required for compression isreduced by utilizing multistage, intercooled, compression of inputstreams at the lowest available temperature.
 39. The process of claim 1,wherein work required for compression is reduced by operatingelectrolysis system at elevated pressure.
 40. The process of claim 1,wherein hydrogen left in the product stream from step (b) is removed bysemi-permeable membrane means and recycled in the process.
 41. Theprocess of claim 1, wherein carbon dioxide in the product stream fromstep (b) is removed by condensation.
 42. The process of claim 1, whereincarbon dioxide in the product stream from step (b) is removed byadsorbtion.